The present invention is adapted for use with a conventional drive system in which a pair of drive sprockets are connected by a flexible drive element such as a drive chain. It is well known that the proper functioning of such a drive system and the operating life of the drive element can be significantly enhanced by maintaining the tension on the two drive element runs between the sprockets such that significant slack does not occur in either run. Tensioning devices of various forms have been developed and used for controlling the tension on the drive element runs during operation. Tensioning devicec can be either mounted within the same housing in which the drive sprockets are mounted, or can be free-floating on the drive element runs. The majority of prior tensioning devices have been adapted for specific drive system applications, resulting in the tensioning devices generally being mounted or secured to a housing or support that is fixed with respect to the sprocket axles.
Tensioning devices are especially useful for tensioning a drive element used in a fixed-center drive system. In such a system, the distance between the shafts upon which the drive sprockets are mounted are not adjustable. Thus, to mount the drive element, it is necessary either to cut the drive element and reconnect the ends after threading the drive element over the pulleys or to provide a belt that is long enough to be looped over the pulleys. In the latter case, the drive element will be slack between the pulleys. A tensioning device mounted around the drive element runs pinches the runs together to take up the slack.
In a system in which the tensioning device is fixed with respect to the sprockets, the drive system housing or support, rather than the tensioning device itself, acts to stabilize motions of the drive element runs that are not parallel to the motion of the drive element during normal operation. No such stabilizing force is present in drive systems utilizing a free-floating tensioning device.
An example of a free-floating tensioning device is presented in U.S. Pat. No. 4,662,862, issued to Matson et al. The tensioning device disclosed therein includes two tensioning members mounted on a flexible drive element such that the runs of the drive element are situated between and contact the tensioning members. The positioning of the tensioning members relative to one another is adjustable to thereby adjust the tension on the drive element runs. In such a system, the tensioning device is the only element other than the drive sprockets exerting force on the drive element runs.